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knuckle head
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On a Lucas 2KF mag, on the points end, there a center screw that'sshorted to ground as a kill switch.......Question, while the engine is runnig, does this same screw have a pulsating current? If so whatsis the voltage? I trying to find out if a modern tachometer can use this voltage signal to trigger tach function... Thanks


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Originally Posted by Hillbilly bike
Question, while the engine is runnig, does this same screw have a pulsating current? If so whatsis the voltage?
That voltage can rise to over a few hundred volts, which is why one of the minimum ratings the capacitor needs is 400 VDC.

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Thanks. most tachs can also use the coil primary that's connected to points, I believe this has several hundered volts when the points open?
And someting else, coil and battery ignitons are DC, Is a Lucas coil AC?


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Originally Posted by Hillbilly bike
Thanks. most tachs can also use the coil primary that's connected to points, I believe this has several hundered volts when the points open?
And someting else, coil and battery ignitons are DC, Is a Lucas coil AC?
Yes, several hundred volts are developed across the points on a "standard" ignition system.

As for AC vs. DC, it's not as simple as that. Even on a "standard" battery ignition system, the current through the primary, and thus the voltage on the secondary, changes with the frequency of the points closing. It's not a simple sine wave that most people think of with "AC", but it's definitely not DC. At, say, 2000 rpm a single-cylinder coil has a pulsed input to it of 1000 rpm, which is ~17 times per second. That is, 17 times per second the 12 V across the coil is shorted by the points closing and it abruptly drops to 0 V. When the points open the voltage recovers to the 12 V, although not nearly as rapidly since it is determined by the ratio of the inductance to the resistance of the coil.

I realize this is more than you wanted to read, but it's less than I should write, and in any case it's entirely your fault for asking about "AC" and "DC" coils.

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Originally Posted by Hillbilly bike
And something else, coil and battery ignitions are DC. Is a Lucas coil AC?

Lucas made both AC and DC coils. Which one are you referring to ?


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knuckle head
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Originally Posted by RF Whatley
Originally Posted by Hillbilly bike
And something else, coil and battery ignitions are DC. Is a Lucas coil AC?

Lucas made both AC and DC coils. Which one are you referring to ?
A writting mistake, I meant are Lucas magnetos ac..
MM ,I was a contruction electrician not an enginner or designer...But I do have a good understandin of igntion as to how they function on a running engine, so say what you need to say..
The electronic tachs need a square wave signals as a trigger.There are adapters for external coil type magnetos and some other ignitons without a Square wave.It connects to the primary wire, not the secondary The adapter also has a inductive pick up if you don't want to cut the wire.
I do want to avoid using a fussy Sitsu tach or the small digital boxes meant for lawn equipment.


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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A problem you may face is you'll have to get the signal via a carbon brush, which is what is used for magnetos with 'off' switches, and it may not be clean enough to provide a good input to the tach that doesn't result in false triggering. However, the brush does connect to the internal primary wire of your K2F. It's just a matter of whether the output is clean enough for your purposes. Surely someone else has gone down that path before and knows what tachometers do and do not work with that as the trigger.

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If I'm reading this correctly (between the lines !) this gets its pickup off the spark plug lead ?
And you can't argue with the price ...
But note I haven't tried it or seen one ...

https://www.wish.com/product/5eba89...h25fAiwEAQYASABEgL5OPD_BwE&share=web

Strobe timing lights can have a similar arrangement.

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If you don't mind me interfering.... You can just buy a small choke wound on a circular former
and run your HT lead through it, put a 1watt 12v zener across the choke and connect + side
to your tacho input and - side to ground that will trigger 90% of those tacho's.

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Originally Posted by Rohan
If I'm reading this correctly (between the lines !) this gets its pickup off the spark plug lead ?
And you can't argue with the price ...
But note I haven't tried it or seen one ...

https://www.wish.com/product/5eba89...h25fAiwEAQYASABEgL5OPD_BwE&share=web

Strobe timing lights can have a similar arrangement.

[Linked Image from ae01.alicdn.com]


I’ve used those with a magneto and they worked.

Last edited by triton thrasher; 03/05/21 10:51 am.

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A friend has a speedhut tach on his 37 Indian Scout with I believe a Hunt magneto. He has a small battery to power the tach. Never paid a lot of attention to how he has it wired but can take a look in a couple weeks. Maybe doesn't apply to Lucas anyway?

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I use Scitsu rechargeable tachos. Just a pick up wire taped to the HT lead
https://www.scitsu.com/


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Originally Posted by NickL
If you don't mind me interfering.... You can just buy a small choke wound on a circular former
and run your HT lead through it, put a 1watt 12v zener across the choke and connect + side
to your tacho input and - side to ground that will trigger 90% of those tacho's.
I used what we called an inductive set up like that on electric equipent so when lets say a pump started, the choke sensed the current and set other equipment into action.
Nick, I'm dumb at times, got a crude diagram? Equus gauges sells a tach with an inductive pick up that clamps on the plug wire.. About $90, but I would rather different brand ....
Originally Posted by Mike Baker
A friend has a speedhut tach on his 37 Indian Scout with I believe a Hunt magneto. He has a small battery to power the tach. Never paid a lot of attention to how he has it wired but can take a look in a couple weeks. Maybe doesn't apply to Lucas anyway?
Mike ,Hunt mags have a coil that will trigger most tachs..
I had the exact same small engine small tach shown above on my double engine bike. It had a hard time with showing a readable rpm until a constant rpm was held for a few seconds...And I prefer traditional analog gauges...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Quote
I had the exact same small engine small tach shown above on my double engine bike. It had a hard time with showing a readable rpm until a constant rpm was held for a few seconds...And I prefer traditional analog gauges.

That makes sense, if you are actually going to try to use it to protect the engine from over-revving.

I’ve seen racing bikes with the rev counter oriented so the needle points straight up at maximum RPM.


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Andy,Does your Scitsu have a steady needle ? I have read complaints on quivering needles at lower rpm and in general being fussy to set up on a twin with a K2F mag. Triton Trasher had trouble with his Scitsu tach and
he has the experience to install it properly..
Not against using a Scitsu .....


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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I’d almost forgotten my inductive Scitsu. That wasn’t yesterday!

Yes it was easily upset. I’ve heard that they give good post-sales support, which I didn’t use, to be fair.


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[Linked Image from i.postimg.cc]

Last edited by triton thrasher; 03/07/21 10:20 am.

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Originally Posted by NickL
Thanks! I'll give it a go...


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“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Have a black wire Scitsu that's for a magneto ignition. Couldn't get it to work on the BSA , so put it on a stock 2005 Harley, works perfectly. Don't figure.


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